Electrostatic controls



March 1, 1960 J. w. DIESEL Y 2,927,255

ELECTROSTATIC CONTROLS Filed July 2, 1954 5 Sheets-Sheet 1 INVENTOR. fjJOHN W.D|ESEL 10: 3M JIM?! March 1, 1960 J. w. DIESEL 2,927,255

ELECTROSTATIC CONTROLS Filed July 2, 1954 5 Sheets-Sheet 2 INVENTOR.JOHN W. DIESEL BY Mw/JM March 1, 1960 J. w. DIESEL 7 2,927,255

ELECTROSTATIC CONTROLS I Filed July 2, 1954 $Sheets-Sheet 3 FIG. 8

INVEN TOR.

.JOHN W. DIESEL BY .iWM/M United States Patent ELECTROSTATIC CONTROLSJohn Diesel, Maplewood, Mo., assignor to Erdco, Inc., Maplewood, Mo., acorporation of Missouri Application July 2, 1954, Serial No. 441,057 12Claims. (Cl. 3 17144 This invention relates generally to electrostaticsand more particularly to electrostatic controls, such as relays.

It has been known for many years that an attractive force is developedbetween two bodies when they bear opposite electric charges, but thecommercial applications of this principle have been few. Indeed, theelectrostatic controls heretofore proposed have been largely laboratorycuriosities of erratic performance and considerable complexity.Accordingly, it is an object of the invention to simplify theconstruction and improve the operation of electrostatic controls. Morespecifically, the invention provides electrostatic controls that arecomparable in function to electromagnetic and electronic devices, butwhich can be operated with better efiiciency, manufactured atsubstantially less cost, made considerably more compact, and moreconveniently connected and assembled in multiple-component apparatus.

The construction of an electrostatic relay has presented seriousproblems to those skilled in the art. The electrostatic or actuatingforces are quite weak and are extremely sensitive to plate spacing, withthe result that the performance is erratic and considerable precision isrequired in manufacture. If the plate spacing were slightly greater thanintended, the plates would fail to attract, and if too close, they wouldreadily be actuated by extraneous secondary effects, such as mightresult from leakage.

Attempts to resolve these difiiculties by the use of high voltage andclose spacing of the plates have not been too successful, because they,lead to a considerable problem in preventing discharge between theplates, such discharge resulting in loss of the electrostatic force. Ithas, therefore, been suggested that the plates be protected againstdischarge with an intervening layer of solid insulation, but thisexpedient has led to even more serious difiiculties. The introduction ofsolid insulation necessitates an increase in the distance between theconductive surfaces of the plates, which consequently weakens theelectrostatic force, and the insulation, if not of considerablethickness, is subject to breakdown under high voltage stresses. Moreimportant, however, are the problems that arise from dielectricabsorption and the property of the insulation to collect asurfacecharge, these factors causing the plates to stick and otherwisemisbehave. In some instances, the plates will fail to release uponremoval of the exciting voltage, and in other instances, the plates willmove in a direction opposite to that intended when excitation isapplied.

There follows a brief description of some of the features ofconstruction and methods of operation utilized in solving these.difliculties. The plate excitation is at rather high voltage, at least athousand volts, but the exciting current is limited to very low values.For example, in the case of a relay of a type suitable for use in acomputer, the plate excitation might be at two thousand volts and thecurrent limited to one tenth of a milliamp, although lower excitingvoltages may be employed at the price of greater exactitude inconstruction "ice (the plates being more closely spaced) or highervoltages may be used if physical size is not too important.

While the plate excitation is at rather high voltage, the plate spacingis very small. in the case of a relay having an effective plate area ofabout one square inch, the spacing of the plates might be onesixty-fourth inch, but may be increased, especially with a correspondingincrease in the plate excitation. Generally speaking, the spacing of theplates will otherwise be determined by the size of the signal which thecontacts are required to interrupt.

In this respect, the invention contemplates that the signals carried bythe secondary or contact circuit will also be at high voltage, at leasta thousand volts and low current, and that the contacts will operate inan ionizable gas, such as air. With such a relay, closed or open circuitconditions are determined more by the distance between the contactsrather than by actual engagement, and the behavior is more analogous tothat of a gas-filled tube than that of a solenoid relay. Such highvoltages (which in the case of a multi-component apparatus would be ofthe same order of magnitude as those used to excite the plates) permitthe establishment of a closed circuit condition, even though thecontacts are not in perfect engagement, a feature which greatlyfacilitates manufacturing procedures and improves reliability. Lowcurrent signals are desired, especially when the contacts are small, inorder to prevent heating to an extent such that an injurious arc eflEectis esablished by burning, melting or vaporization of the contacts.High-voltage low-current signals have additional advantages when thecircuit components are formed by printed circuit techniques.

As pointed out, one of the fundamental concepts of this invention is theuse of high voltage and close spacing of the plates, features which haveheretofore been impractical, but for the introduction of a solidintervening insulator for preventing discharge between the plates, whichinsulator, in turn, has resulted in additional dithculties of an evenmore serious nature. The invention contemplates, in a preferredembodiment, that there will be no such solid insulator, but thatneutralizing discharge between the plates will be controlled by highresistance within the control itself. Preferably, one of the plates isformed, at least in part, of high resistance material, and discharge islocalized over certain areas of the plates, thc arrangement being suchthat other areas of the plates will be maintained at difierentpotential, despite the presence of a charge transfer. This arrangementserves to prevent the uncontrolled accumulation of charges of a typethat would produce malfunctioning of the control, and also permits veryclose spacing of the plates.

Additionally, the invention contemplates the provision of a highresistance shorting connection between the plates, the arrangement beingsuch as to permit adequate accumulation of charges on the plates inresponse to plate excitation and yet quick removal of such charges inresponse to the withdrawal of the exciting voltage. This shortingconnection or release circuit has the additional function ofdiscriminating between true exciting signals and extraneous chargesresulting from leakage, which if permitted to accumulate, might resultin false actuation of the control.

While the above principles might be utilized in a1 wide variety ofstructures of diiiering application, the invention further provides animproved relay structure especially adapted for multi-componentapparatus. Briefly, such a relay comprises a plurality of'overlyingpanels of insulating material, upon which panels the plates, circuitparameters and leads are formed as conductive coatings by printedcircuit techniques. One of the panels may be a relatively fixed rigidmember, whereas an opposite panel may be mounted to flex toward and t)away from the fixed panel in response to the presence and absence ofplate excitation. The plates are formed on opposed faces of these panelsas areas of the order of a square inch, contacts being actuated byrelative movement of the panels.

in one embodiment, the movable panel includes a flap, the free end ofwhich is normally spaced from the fixed panel so that the inherentresilience thereof supplies the bias for opening the contacts andseparating the plates. This flap is enclosed in a fixed frame-like cerand is limited in outward movement by a fixed overr ing shielding panel.A movable contact is secured at the free end of the flap for cooperationwith a fixed contact mounted over the other panel, a low-resistanceplate being formed by silver paint on the flap and a high-resistancecoating being formed on the other fixed panel v. .h carbon paint, Withthis arrangement, the free end portion of the movable plate is preventedfrom engaging the highresistance fixed plate, although the plates mayengage one another in their center portions. The exciting circuit leadfor the high-resistance plate then extends therefrom adjacent the freeend of the flap. Leads for the movable contact and plate may extend onopposite faces of the flap to the fixed end thereof; and ahigh-resistance release circuit is provided for shorting the plates.

The terminals for the plates and contacts are brought out at the sidesand ends of the unit; and these terminals may extend across the edges ofthe unit in order to make connection with similar units stacked one uponthe other or with a suitable base upon which units are secured. It willbe observed that this laminar panel construction simplifiesmanufacturing operations inasmuch as such panels may be readily die cut,printed and assembled with automatic machinery.

It may also be noted that the electrostatic controls of this inventionare adapted for use as signal or information storage devices and otherapplications, which will be subsequently described in detail.

Other features of the invention will be in part apparent from and inpart pointed out in the following detail description taken in connectionwith the accompanying drawings, in which:

Fig. 1 is a circuit diagram of a relay that embodies features of theinvention, parts being shown in position prior to excitation;

Fig. 2 is a more detailed cross-sectional view, showing the relay arm inits actuated position;

Fig. 3 is an exploded view of certain insulating panels Which areassembled to form a relay;

Fig. 4 is a view similar to that of Fig. 3, but showing the reversefaces of the insulating panels;

Fig. 5 is a cross-sectional view of an assembled relay taken on the line55 of Fig. 6;

Fig. 6 is a cross-sectional view taken on the line 66 of Fig. 5;

Fig. 7 is a cross-sectional view taken on the line 77 of Fig. 5;

Fig. 8 is a top plan view of a bottom panel illustrating an alternativeembodiment of the high-resistance plate;

Fig. 9 is a top plan view of a relay-arm panel showing a constructionfor use where a relay is to control a large number of secondarycircuits;

Fig. 10 is a simplified circuit diagram of a valve type of control;

Fig. 11 is a View similar to that of Fig. 10 but showing a control forintroducing a time-delay in the passage of a signal;

Fig. 12 is a circuit diagram of a control suitable for short-termtemporary storage;

Fig. 13 is a view similar to that of Fig. 12, but showing a control thatmight be used for comparatively longterm temporary storage;

Fig. 14 is a circuit diagram of a control wherein the relay arm iselectrically biased in either direction of movement; and

Fig. 15 is a detail sectional view somewhat similar to Fig. 2, butillustrating an arrangement for use in a double-throw relay.

Initially, it should be understood that in the field of electricalcontrols, such as relays, one has been limited for practical purposes toa selection between electromagnetic and electronic devices. In manyapplications, particaularly multiple-component apparatus, neither typeof device is entirely satisfactory. For example, an electromagneticcontrol is expensive (the cost of a reliable solenoid relay being of theorder of one dollar), bulky (the practical size being not less than onecubic inch), and ofttimes not too reliable (because of failure at thecontacts from dust or corrosion). Moreover, a solenoid draws asignificant exciting current.

Electronic controls are faster, principally because they have only todeal with the insignificant mass or inertia of an electron as comparedwith the substantial Weight of an iron armature in a magnetic device. Onthe other hand, electronic components are also expensive and spaceconsuming. In addition, an electronic device of the thermionic emissiontype requires a substantial filament heating current, and when suchcomponents are used in large numbers, they not only consume considerablepower, put generate appreciable heat.

These factors are especially important when the components are assembledto form apparatus of the type used for such purposes as internalstorage, addressing, data switching and arithmetic computations. In thisarea, a given piece of equipment will include a large number ofcomponents, hence the components should not only be inexpensive, smalland operate with little power, but they also should be convenient toassemble and con nect together. In relation to the last point, printedcircuits offer great promise, but are not easily connected to solenoidrelays or vacuum tubes. Also, printed circuits frequently have asignificant amount of resistance and are therefore not adapted to carrythe substantial exciting current of a solenoid or filament-heatingcurrent of a vacuum tube.

Furthermore, since solenoids operate with relatively low-voltagehigh-current signals, diificulties are frequently encountered fromimperfect closure of the contacts. A small particle of dust or slightcorrosion at the contacts may prevent relay of the signal, a matterwhich is especially serious in computer applications because error isintroduced in the output information and because it is extremelydifiicult to locate the cause of the trouble. On the other hand,electronic 'or vacuum tube components suffer from the serious limitationof controlling only one circuit at a time, a. fact which leads toconsiderable expense in some applications, 'such as digital computers.

For these reasons, it is customaryin the digital computer field to usemotor-driven gear devices when cost and size are important and speedunimportant, or to use vacuum tube devices where speed is the primaryconsideration and where cost, size and complexity are of nominalconcern. Between these two types of machines, there lies a wide area inwhich there has not been much success in applying solenoid or electroniccomponents. Perhaps some experimenters have considered electrostaticcontrols, but the difficulty is that while the principles are of someantiquity, the structures heretofore proposed have not beencomparable'in a practical sense with more familiar electromagnetic orelectronic controls.

Various proposals are found in the art, among which may be noted the useof rigid m'etal electrodes separated by an air gap (Patent No. 749,775),conductive plates separated by a solid resilient dielectric (Patent No.1,834,786), spaced metal electrodes coated with insulation andhermetically sealed (Patent No. 2,175,354), piezoelectric crystals(Patent No. 2,182,340), and liquid dielectrics'(Pate'nts No. 2,419,111and No. 2,417,850).

The simplest type of control-consistsof two relativelymovablerigidmetalplates which are separated by an air fruitful. -device wherein slightmovement of the relay arm is caused to trigger other mechanism, whichactually closes athe contacts, but such a tripping device is complicated:and must be reset after each operation. The other tack gap. Thedifiic'ulty with thisarrangentent isthat the plates must not only beinitially spaced to prevent loss of potential by discharge between theplates, but they must be prevented from approaching one another to anextent that they would so discharge. If the distance between the platesis large, however, the electrostatic attractive force is very weak. Itis of no help to increase theexciting voltage, because a correspondingincrease in plate separation is necessary in order to preventinadvertent discharge, and the electrostatic force falls off rapidlywith an increase in the plate spacing.

Consequently, it is not surprising that resort has been made to the useof a solid dielectric between the plates, but this approach has alsoproved unsatisfactory. Thin dielectrics are subject to breakdown, and athick dielectric increases the spacing and limits movement of theplates. The'dielectric has a further serious disadvantage in thatsecondary charges collect on the surface, and such extraneous chargescause the plates to stick and otherwise misbehave. For example, when apositive plate moves against or even near an insulated surface, apositive charge is transferred to the insulation. When the electrodesare again excited at a later time, this positive charge upon theinsulation may well cause the positive electrode to move away ratherthan toward the negative electrode. It may be noted that the problem ofdealing with secondary extraneous charges is much more serious than isgenerally recognized, especially when attempt is made to build a deviceof small size.

Finally, there is the problem presented by the secondary circuit of arelay type of control. Inasmuch as the mechanical forces are weak andthe electrode spacing rather critical, particularly in prior devices,the art has been faced with a problem of imperfect closure andinadequate separation at the contacts. This difliculty has led the artin two paths, neither of which has been very One approach involves theuse of a tripping taken makes use of contacts that are initiallyseparated ;a very slight amount so that the least possible motion isrequired to close the circuit. The difliculty here is that only signalsof very low voltage can be handled by the contacts.

Referring now to the drawings,.Fig. l illustrates certain electricalaspects of an electrostatic relay having a relatively fixed conductiveplate 1 and a fixed contact 3. A movable relay arm 5 overlies the fixedplate, and this arm carries a conductive plate 7 on its lower surfaceopposite the fixed plate 1. A movable contactv 9 is mounted at the freeend of the relay arm opposite the fixed contact 3 and in insulatedrelationship from the plate 7. The relay arm may be fixed at its otherend 11 and is normally biased away from the fixed plate, but this biasis adapted to be overcome by the attractive force developedelectrostatically between the plates. Connections to the'movable plate 7and movable contact 9 may then be made at the fixed end of the relay armon opposite faces thereof.

Referring to Fig. 2, the fixed plate 1 is secured to the upper face of.a relatively rigid insulating member 13, and

the movable plate 7 is a flexible conductive coating on the relayarm 5,which is formed of resilient insulating material. The member 5 is biasedoutwardly, as by a wedge member 15adjacent the fixed end 11, so that theplates 1 and 7 and contacts 3 and 9 are normally spaced apart. The plateis sufiiciently flexible, however, so that the arm bends resilientlyover the wedge 15 to close the contacts when voltage is applied acrossthe plates. The intervening portion may also bend so that the movableplate7 engages the fixed plate 1 at locus X. A flexible conductor 17leads from the plate at the fixed end thereof,

i overly weakattractiveforce and the incorporation of a 6 whileaflexible conductor 19 leads from the movable contact 9 over the uppersurface of the relay arm to the fixed end thereof. This fixed end may besecured by an overlying member 21.

In addition, the relay includes an insulating member 23 located abovethe relay arm 5 to limit its outward movement. The lower face ofthis-insulating member 23 may carry a conductor 25 which is coextensivewith the contact conductor 19, and the upper face may carry a plate 27which is generally coextensive with the plates 1 and 7.

Returning to Fig. l, the plates are shown to be connected by an excitingcircuit EC to a DC. power supply designated by the box V. The positiveterminal of this power supply is connected through a switch S to themovable plate 7, whereas the negative terminal andfixed plate 1 areconnected to one another and may be grounded. 1

The invention contemplates'that the plate excitation will be at highvoltage and of low current, an output of two thousand volts beingsuggested for relay controls of-the type described herein. The currentoutput of this source may be relatively low, adequate safety beingachieved by limiting the current output to a few milliamps., as by usinga power supply having high internal resistance IR.

The exciting current is-chiefly limited by the resistance or impedanceof the control itself, and indeed, satisfactory relay controls have beenoperated on currents as low as one-tenth of a milliamp, although thisdoes not exclude even smaller operating currents. This impedance is inpart in series with and in part in parallel with the plates. The seriesresistance, in turn, may be in part or entirely internal with theplates, such internal resistance being represented by the legend PR.

As indicated previously, the movable plate 7 bends to approach or -evenengage the fixed plate 1. In the absence of an intervening dielectric orvacuum, a transfer of charge would occur when the relay arm is in itsactuated position, and such a transfer would tend to result in dischargeof the plates, especially when both plates are formed of metalor otherhigh conductivity material. If the plates discharge, the relay arm isreleased, and when it swings outwardly, the discharge path isinterrupted and the plates would recharge until the relay arm is againactuated. Such a fluttering of the relay arm is not desired, and forthat reason, it has generallybeen deemedv necessary to prevent platedischarge by-use of a solid dielectric or bylarge plate separation.Neither of these approaches; is considered satisfactory,- however,inasmuch as-a large separation of the plates results in an dielectricleads to difficulties from stray charges collected on or inthe'dielectric.

The present invention recognizes-that such discharge need not becompletely prevented and that a conductive condition is indeed necessaryif undesired accumulation of charges is to be prevented. In contrastwith prior practices, there is provision fora transfer of chargesbetween the plates, but it is controlled, as to rate, direction andlocation. The arrangement is such that a voltage differential ismaintained over some portions of the plates despite the flow of chargeand loss of potential at other portions, such as at locus X. This may beaccomplished in various ways, one of which involves mounting the relayarm, as shown in Fig. 2, so that a portion of the movable plate at thefree end of the relay arm is prevented from" approaching the fixed plateas nearly as the center portion X. The exciting circuit is thenconnected to the fixed plate 1 at an adjacent point so that when chargeflow develops at the locus X, it will pass through a portion of thenegative plate in a direction primarily parallel to its surface towardthe free end of the relay arm. Finally, the fixed plate is designed toprovide considerable resistance PR between mamas 7 the locus X and theend portion, where the plate is connected to the exciting circuit. I

In the absence of a transfer of charge directly between the plates, thefull output of the supply V would appear uniformly across the plates.When a flow does develop at X. a voltage gradient occurs across theplates from the locus X to the end portion of the plates, and theresulting electric field is sufficient to maintain the relay arm in itsactuated position.

The internal plate resistance PR can be conveniently supplied by formingthe fixed plate -1 of high resistance material, such as a suspension ofcarbon granules in a suitable binder. A rather high resistance isdesired; for example, the resistance between the point X and theterminal connection 29 might be thirty megohms; in which event, theplate current would be less than one'tenth of a milliamp. If additionalseries resistance is desired. it may be supplied by extending thehigh-resistance negative plate 1 beyond the positive plate 7, as will beapparent hereinafter to provide a resistance DR. For relays of the typeto be described in detail, a total series resistance of thirty to fortymegohms seems to be satis factory, but these values obviously can bevaried considerably.

If the series resistance is too high, however, the control may becomeunreliable. Also, the plates may not charge at an adequate rate. On theother hand, too low a resistance will result in excessive sparking atthe plate surfaces and burning of the plates. While the highresistanceplate may be formed in various ways, a suspension of conductive granulesin a body having dielectric properties may have special advantages,which are not as yet entirely understood.

In the past, it has been customary to assume that when the switch S isclosed, the full voltage of the source V is immediately impressed acrossthe plates, thereby causing an attraction of the plates. Actually,closure of the switch S merely establishes a circuit which permits acharge to accumulate on the plates. The amount of charge is determinedby the exciting voltage and the capacitance CP of the plates, althoughthis capacitance varies as the plates move together. When the switch Sis opened and the excitation removed, it has similarly been assumed thatthe plates immediately swing apart. With the control herein described,at least, such an assumption is not entirely justified. Indeed, it isnecessary to clear all of the accumulated charges, if the plates are torelease upon removal of the plate voltage and if other malfunctions dueto these residual charges are-to be prevented. In order to prevent thesedifficulties, the invention contemplates the provision of a release orshorting connection between the plates to remove the charges accumulatedin the conductive portions thereof. Charges that otherwise might tend tocollect in or on a dielectric are carried away through the resistance ofconductive granules of the fixed plate.

In the illustrated embodiment, this shorting connection is a releasecircuit RC connected in parallel with the plates in the excitingcircuit. As such, the circuit RC also acts as a short across the powersupply V, hence a resistor RR is connected in the release circuit tominimize the drain effect of the release circuit and insure a potentialdifierence at the plates. The magnitude of the resistance RR should notbe too high, however, it it is to be effective in quickly releasing theplates. a typical relay, the parallel resistance RR might be of the sameorder of magnitude as the series resistance PR. described previously.

The release circuit RC has an additional important function in that itlargely eliminates, difliculties that would otherwise be encounteredfrom general leakage throughout the system. Such leakage is almostimpossible to avoid in a device that is not hermetically sealed orotherwise protected against high humidity conditions,

and it is especially troublesome with electrostatic devices.

With the present invention, leakage will not result inadvertentactuation of the relay under normal conditions. Insofar as extraneoussecondary positive charges tend inadvertently to build up on thepositive plate 7, they will be withdrawn through the release circuit RCbefore they can accumulate to an extent that would result in falseactuation of the control.

While the resistance of the release circuit is substantial andinterferes with rapid transfer of such charges, generally speaking,leakage is a relatively slow process. Consequently, the release circuitmight be said to have the function of discriminating between truesignals (which involve relatively large currents, and fallacious signalsresulting from leakage through the system (which are generally of verylow current values).

it may also be desirable to provide an inductor RL in the releasecircuit as part of the parallel impedance. The inductor functions toprevent an excessive drain through the release circuit RC when theswitch is first closed and the exciting current is initially high. Inother words, the inductor RL increases the eifective impedance of therelease circuit when the plates are initially excited. After some delay(determined by the amount of inductance and resistance in series withthe inductor), the eifect of RL fades and the release circuit draws alarger current. This is permissible, however, because the plates willhave been substantially charged in the interval. The inductor RL mayalso serve to increase the release speed of the relay upon thede-excitation of the plates.

A somewhat similar effect could be obtained by connecting a capacitor inseries with the plates, the capacitor being by-passed by a highresistance element or having some leakage.

It may additionally be desirable to provide a capacitor C in theexciting circuit across the voltage supply V when the supply hasconsiderable internal resistance IR. The significance of the capacitor Cis that a substantial current is initially required to charge the plate,but once charged, the current requirements are relatively low, beingonly that resulting from discharge between the plates and drain throughthe release circuit RC. The capacitor C is a storage device, which willsupply the initially heavy charging current without overloading thevoltage source when the switch S is first closed.

Referring now to the contact or secondary circuit CC, the inventioncontemplates that the signals carried by this circuit will be of asufliciently high voltage to permit establishment of a closed circuitcondition, even though the contacts are not in perfect engagement, thehigh voltage tending to cause the signal to jump a slight gap betweenthe contacts or overcome contact impedance that would otherwiseinterfere with passage of the signal. With this arrangement, the openand closed circuit conditions are determined by the distance separatingthe contacts rather than by actual physical engagement of the contacts.In using this principle, it is necessary to have an ionizableatmosphere, and for that reason, there should not be a high vacuumcondition at the contacts. On the other hand, the current of thesesignals should be low enough to prevent contact heating such that an arcdischarge occurs between the contacts. The behavior of the device, inthis respect, is comparable to a gaseous-discharge vacuum tube, but withthe difference that the circuit is opened by increasing separation ofthe contacts rather than by an inverse plate voltage.

In computer applications involving a series of electro- Static l h si acarried y e s ondary c rcu uld, be of h s me olt g an c r-ren theserequired to actuate the plates. It may be noted that the contactproblem, while always important, is critical in the case of computersand the like, because failureat even a single contact point cannot betolerated. It might be said that in a computing apparatus, thev contactsshould be eager to carry a signal (as in the disclosed device) ratherthan reluctant (as in solenoid relays).

Utilizing the above principles, it is possible in an electrostatic relayto have (1) a lightweight sensitive relay arm, (2) close spacing of theconductors, (3) close spacing of the plates, and (4) a compactarrangement of a series of relays, these being features which are ofprime importance in many applications. Heretofore, the first threeconditions or features have been impractical to achieve because ofinterference or leakage between the parts of a given control unit. Thefourth abovementioned feature also tends to cause interference whenunits are stacked close together, as they normally would be in multiplecomponent apparatus.

For instance, a positive relay arm may be undesirably attracted by thenegative plate of a relay located immediately above. If the outer caseof the relay is at ground potential and in close proximity to the relayarm, the arm might even be attracted by the case when excitedpositively. This difficulty is herein overcome by reflecting the chargeon the relay arm in a plane opposite the fixed electrode. Referring toFigs. 1 and 2, the plate area 27 on the member 23 is connected, in.parallel with the positive plate 7 so that both of the elements 7 and 27are positively charged upon closure of the switch. To some extent, therelay arm is thereby repelled by the plate 27, although in anothersense, the plate 27 serves merely as a shield between stacked relays.

; A similar undesired effect may be caused by the contact lead 19, andis herein prevented by the conductive strip' 25 on the member 23. Thisconductive strip 25 is connected in parallel with the strip 19 so that acharge differential will not develop therebetween. Also, the contactsthemselves should be of small area in comparison with the plate areas,so that the attractive force between opposed contacts is at a minimum.Large contacts are not required in the described relay, inasmuch as thecontact currents are relatively low and have an insignificant heatingeffect.

Reference is now made to Figs. 3-7 for a description of a specificstructure which might be used as a relay in a digital computer and othermulti-component apparatus. The device comprises a plurality of flat,generally rectangular insulating members for carrying the conductiveelements. In a device for controlling ten secondary'circuits, the panelsmeasure approximately three inches in width and length, and are ofvarying thickness and composition. A bottom panel 101 and top panel 109are .010 inch Vinylite (polymerized vinyl chloride resin), a relay-armpanel 105 is .005 inch Vinylite, a contact member 103 is .020 inchVinylite, and a spacer frame 107 is .060 inch laminated phenolic orstyrene resin. Such insula'ting members would be die cut from sheetstock, the conductive elements being formed thereon using printedcircuit techniques. sembled in stacked overlying relationship and aresecured together, as by bolts 111 through corner apertures 113.

The panel 101 constitutes the base of the device and serves as a supportfor the fixed plate, which is formed as a coating 115 of conductivepaint. Conductive paints being known in the art, they are not describedother than to note that they customarily comprise a suspension ofconductive granules in a suitable binder. The resistance of the paintand resulting co'ating is to some extent controlled by the proportionsand character of the ingredients, silver granules being generally usedwhere high conductivity or low resistance is desired, and carbongranules being utilized for high resistance paint.

In the disclosed embodiment, the fixed plate 115 is formed as a highresistance coating measuring one and three-eighths inches in width andone and three-fourths inches in length. The paint is of a type providingapproximately one hundred seventy-five megohms per square inch, thisbeing a term of art indicating that a coating one inch in width andlength normally has a resistance of the stated value between oppositeedges.

The coated members are then as-' 10 The plate area extends close to anend 117 of the device and a high conductivity lead is formed as a strip119 to extend across that end of the plate to an adjacent corneraperture 113. A connection to ground and to the negative terminal of theexciting source is then made through the associated bolt 111 (Figs.5-7).

It may be observed at this point that the terms high resistance and highconductivity (or low resistance) are used in a relative sense inasmuchas printed leads formed with silver paint will have appreciableresistance. It is only intended that the voltage drop in the leads arenominal in relation to the drop at a resistive plate or across one ofthe resistances referred to. Also, a distinction is made betweenresistive material, such as carbon paint, anda semi-conductivedielectric, such as stone or organic membranes, the latter having only avery slight leakage usually aided by absorbed moisture. Semiconductivedielectrics are considered impractical because of their very high volumeresistivity, if such materials can really be considered to have aresistance.

The plate 115 may in part extend beneath a thin piece 121 of insulatingmaterial, which is located at the end 117 of the device to minimizeleakage between the fixed plate and fixed contacts. This covered portionof the plate 115 serves as the series resistor DR referred to earlier.The resistor RR of the release circuit is a relatively narrow strip 123of high-resistance conductive paint extending over the panel 101outwardly of the plate 115 and inwardly of the side edge 125 of thedevice, and a lead 127 extends therefrom to the side 129 of the device.The width and length of this strip, as well as the character of thepaint, determine the resistance in the release circuit, which would beapproximately thirty megohms in the described embodiment.

The contact member 103 has a central opening for accommodating the relayarm of the device, and up-. wardly-facing contacts 131 are mounted alongthe margin of this opening and high-conductivity leads 133 extend to theadjacent end 117 of the device. Although conductive paints may not beentirely satisfactory for contact purposes, there are other techniquesknown in the art which may be utilized in forming a lightweight contactwhich will withstand the slight heating to be ex-' pected from sparking.Although some degree of uniformity is desired when there are severalcontacts, the problem is not what it is in conventional devices wherewiping engagement is generally necessary to establish a closed circuitcondition and where contact rebound is a matter for concern.

The'relay-arm panel 105 is out about the margins 117, j

125 and 129 to form a resilient flap 135, the free end ofwhich extendsover the fixed contacts 131 as a relay arm. The movable plate is ahigh-conductivity coating 137 over the lower face of the flap, the plateextending from a point short of the free end to the other end 139 of thedevice, where it is connected to a strip 141 of highconductivity paint.The conductor 141 extends over the fixed marginal portion of the panelto the side 129, so

as ultimately to make a connection with the lead 127 of thereleasecircuit.

Movable contacts 143 are mounted on the free end of theflap forcooperation with the fixed contacts, and leadforming strips 145 ofhigh-conductivity paint extend over the upper face of the flap to theend 139 of the device.

Inasmuch as the flap is fixed during use, it may be desirable toincorporate a plasticizer in the conductive paint forming the coatings137 and 145. In assembly, a narrow piece 147 of insulating material issandwiched between the flap and the bottom panel' 101 adjacent the fixedor hinged end so as to urge the relay arm 135 upwardly. Movement of therelay arm is accommodated by the surrounding frame-like spacer 107 andis limited by engagement with the overlying top panel .109. When severaldevices are to be. stacked one upon are assembled together.

the other, the panel 109 may be coated to shield the several devicesagainst electrical interference with one another. Conductive strips 149on the lower face of the panel 109 extend over the contact leads 145 andare electrically connected thereto at the end 139 of the device, whereasa conductive shield 151 on the upper face of this panel is connected tothe movable plate by a lead 153 at the side 129 of the device.

It will be noted that the free end portion of the flap 135 is projectedthrough the contact member 103 and also curled outwardly somewhat, thelatter being desirable in that it permits relatively close spacing ofthe plates 115 and 137 with rather wide spacing at the contacts. Contactclosure is achieved both by downward movement of the flap and by atendency of the flap to straighten under the electrostatic forcesapplied across the plates. The contact member 193 prevents the platesfrom coming into physical engagement over their entire surfaces,however. The inherent resiliency of the flap supplies the bias forotherwise opening the contacts and separating the plates, the wedgingstrip 147 being adjustable to vary the amount of bias, but in thefinished device, this wedging strip is secured so that the device may beoperated in any position.

The disclosed arrangement also provides for connection of the electricalelements merely by assembly of the panels. To that end, connectingelements of high-conductivity paint are formed on the several insulatingmembers to extend across the edges thereof and partially over themargins. Connecting elements 155 provided at the side 129 are aligned sothat the leads 127, 141, and 153 become connected with one another whenthe members Connecting elements 157 are provided at the end 117 inalignment with the leads 133 for the fixed contacts. Similar connectingelements 159 located at the other end serve to connect the leads 145 forthe movable contacts and the overlying coextensive shielding strips 149.This arrangement is not only desirable in facilitating the constructionof a single unit but also facilitates the assembly and connection ofseveral units, whether they be stacked one upon the other or mounted ona panel previously ruled with conductive strips adapted to register withthe connecting elements 155, 157 and 159.

Whereas the negative plate 115 in the embodiment of Figs. 3-7 is shownto be formed as a coating of uniform resistance, different arrangementsare possible. For example, as shown in Fig. 8, the coating on a bottompanel 201 may be constituted by contiguous strips 215 of highresistancepaint, the strips being of varying width and being formed fromhigh-resistance paints of differing resistance values. Similarly, therelease circuit may be of a different arrangement. For example, themovable plate may extend at its fixed end into direct overlappingengagement with the high-resistance fixed plate, so that the latterprovides the high-resistance for the shorting connection.

Fig. 9 illustrates an alternative arrangement which might be used wherea rather wide relay arm is required to accommodate a large number ofsecondary circuits 245. In this instance, one or more slots 263 is cutin the center of the flap 235 to relieve buckling and facilitate escapeof the air cushion between the plates as the relay arm is actuated.While there are not theoretical limits to the size of the relay arm,present experience seems to indicate that a relay arm one-eighth inch inwidth and one-half inch in length is about the smallest practical size,and a relay arm three inches in width and two inches in length is aboutthe largest useful size. These figures are, given merely in the natureof suggestion, however, and should not be taken as limiting inasmuch asfurther development work may extend the range considerably.

Fig. 9 also illustrates an arrangement wherein the free end of the relayarm is slit at 265 to provide resilient contact fingers 267 carrying themovable contacts. It has been found that this type ofrelay arm isespecially de- 1'2 sirable when a large number of secondary circuits arecarried on the relay arm.

The arrangement shown in Fig. 1 is a simple control for relaying asignal from the source V to a load L upon closure of the switch S, butthere are many other applications of the invention. In Fig. 10, there isshown a valve type of control which is adapted to pass a signal from theterminals T-l to the terminals T-Z while preventing passage of a signalin the reverse direction. In such case, the movable contact MC isnormally spaced from the fixed contact FC and is connected to themovable plate MP, so that the open contacts block transfer of chargefrom the terminals T-2 to the plates, but permit charging of the platesMP and PP from the terminals T-1.

Fig. 11 illustrates a similar device which is adapted to introduce adelay in the passage of a signal from the input terminals T-1 to theterminals T-2. In this embodiment, a resistor R1 is connected betweenone of the input terminals T-1 and the movable plate MP. The resistorR-1 serves to delay charging of the plates so that the contacts MC andFC do not immediately close upon application of a signal to the inputterminal T-l. The plate capacitance PC is rather low, hence theresistance R-l should be of a very high value.

Referring to Fig. 12, there is shown a hold type of control which mightbe used for storing information'over a short period of time. Inputterminals T-1 are connected to the movable and fixed plates MP and FF,whereas the contacts MC and PC are connected to output terminals T-2. Inthis instance, the release circuit RC includes a normally open switchS-1 and may or may not have a series resistor RR. An input pulse resultsin attraction of the plates and closure of the contacts. The platesremain actuated upon discontinuance of the input, immediate dischargebeing prevented by the open switch 8-1 in the release circuit. Theclosed condition of the contacts hence serves to indicate the priorexistence of a pulse received at the input terminals, although suchpulse is of a transient character. This control would be used forshort-term storage because leakage between the plates would utimatelyresult in their release. Otherwise, release is achieved by closing theswitch S-1.

Fig. 13 illustrates a hold circuit which might be used for storage overlonger periods of time. As before, input terminals T1 are connected tothe respective plates and output terminals T-2 are connected to a firstset of contacts MC-l and FC-1. A second movable contact MC-2 isconnected to the movable plate and an associated fixed contact FC-2 isconnected through a switch 8-2 to the positive terminal of a voltagesource V-l. This voltage source is otherwise connected to the fixedplate FF. In operation, a pulse applied to the input terminals resultsin actuation of the plates and closure of both sets of contacts. Thesecond set of contacts then establishes a charging circuit from thevoltage source V-l across the plates so that they will be held in theiractuated position upon discontinuance of the input at T-l. The contactswill remain closed until the switch 8-2 is opened to permit discharge ofthe plates through the release circuit RC.

Fig. 14 discloses a further embodiment which might be employed where itis desired to have little, if any. mechanical bias on the movable plateMP. As in Fig. l, the positive terminal of an exciting source V isconnected through a switch S to the movable plate, and the negativeterminal is connected to a fixed plate FP-l, a high resistance releasecircuit RC being connected across these plates. A second fixed plateFP-Z is mounted over the movable plate and is permanently connected tothe positive terminal of the exciting source V. It will be understoodthat the movable plate MP has conductive surfaces which face bothupwardly and downwardly for cooperation respectively with the plates FP2and FP-1. Also, the plate FP-Z, as well as the plate FP-l, would beformed of high-resistance paint.

When the switch 8 is open, there is little, if any, volt agediflerential between the movable plate MP and the lower fixed plateFP-l, but there exists a substantial voltage difference between themovable plate and the upper fixed plate FP-2, which difference causesthe movable plate to be drawn upwardly. When the switch S is closed, theplates MP and FP-2 lose their potential dif' ference and a voltagedifferential appears between MP and FP-l, thereby causing the movableplate to be drawn downwardly.

It will additionally be apparent that normally-closed or double-throwrelays may be designed in accordance with the principles of thisinvention. For example, Fig. 15 illustrates a possible arrangement for adouble-throw relay. In this instance, the relay arm 305 has upper andlower movable plate areas 307. Movable contacts 309 are mounted at theend of the arm, but the lead 319 therefor is embedded in the relay armin insulated relationship from the plates 307, as by using a laminatedtype of construction. A pair of fixed contacts 303 are spaced onopposite sides of the movable contact 309, and resilient biasing fingers304 project inwardly from the fixed contacts so that the relay arm isnormally biased to a center position clear of the fixed plates 301 andfixed contacts 303.

From the foregoing, it will be apparent that the invention provides acontrol that can be manufactured at small expense in comparison topresent devices used for equivalent purposes. The insulating members orpanels can be die cut and coated at high rates of production, and it ispossible that conventional printing machinery may be used for thispurpose. Assembly of the panels is obviously a very simple operation,and the assembled units may be readily stacked or mounted upon panels toform multiple-component apparatus. The block-like shape and the smallsize of the units also permits a very compact arrangement.

Efiiciency is also excellent, as a unit of the type described draws onthe order of one-tenth of a milliamp when the input is approximately twothousand volts, the power consumption being only one fifth of a watt.Inasmuch as the currents are of such low values, the high voltagesignals are practically harmless.

Generally speaking, it will be desirable to hold the plate spacing to assmall a distanceas possible, bearing in mind the voltage that must beinterrupted by the contacts. At the present time, plate spacing of theorder of one sixty-fourth inch is found practical, particularly when therelay arm is curved slightly as shown in Fig. 5'

so as to be flattened by the pull between the plates when excited. Thecontact separation could also be increased by extending the relay arm orby using other well-knownprinciples. There being no necessity for thecontacts to be tightly pressed together, the relay arm and other partsmay be made of lightweight thin material. This feature of constructionand the absence of series inductance permits a high-speed operation, ascompared with solenoid relays which have relatively heavy armatures andconsiderable series inductance.

Additionally, it is to be observed that the relay arm is entirelyenclosed in the devicev illustrated and described in connection withFigs. 3-7, and it will be apparent that the chamber containing the relayarm may be hermetically sealed to provide a controlled atmosphere.

Such an arrangement may be desired when high relative humidity producesleakage in excess of that which can be adequately handled by the device.A sealed condition is readily achieved by compressing the insulatingpanels or by coating the outer surface of the device with lacquer.

As has beenindicated, relays of the character disclosed herein areparticularly useful in digital computers, business machines and thelike. In contrast to present business machines which make use ofmagnetic tape or punched cards, it is contemplated that the inputinformation for a machine using components of the type decr herein o d.b um .li. d.. sra a s sn s? '14 tape marked'rnerely with a lead pencilor conductive inle, this practice being permissible because the signalsused can be conducted by this marking or other type of mark ing whichwould not be suiiiciently conductive for solenoid or tube controls.

A typical card might have indicia boxes arranged in ten rows (toaccommodate numerals zero through nine) and a number of columnscorresponding to the number of digits to be handled. At other points,the card would be marked to indicate to the machine What type ofoperation is required. The cards would then be conveniently read, as bybeing fed against a drum on which a plurality of paired contacts wouldregister with the various boxes on a card. Where a box has been markedwith a con.- ductive material, a circuit would be established thereby,through the paired drum contacts for that box. One of the advantagesconnected with this practice is that the cards could be marked manually.

From the foregoing description, it is apparent that those skilled in theart will understand the structure, function, and mode of operation ofthe invention herein disclosed, and appreciate the advantages thereof.Although several embodiments have been disclosed in detail, it is to beunderstood that the invention is not limited thereto, but the drawingsand description thereof are to be understood as being merelyillustrative. It is realized that many modifications and variations willpresent themselves to those skilled in the art without departing fromthe spirit of this invention or the scope thereof as set forth in theappendedclaims. I

It will be understood that the term fully conductive is used indescribing the plates as being conductive over their entire effectiveopposed surfaces, so that no stray charges can accumulate thereon, evenat limited areas. The plates are conductive in the sense that straycharges cannot accumulate, although the degree of conduction may below-in fact, the resistance of the plate circuit is quite high and atleast one of the plates is preferably formed of high resistancematerial.

Having thus described the invention, What is claimed and desired to besecured by Letters Patent is:

1. Electrostatic relay apparatus comprising a pair of opposed fullyconductive plates mounted for relative movement toward and away from oneanother, a pair of,

cooperating contacts at least one of which is mechani-' cally actuatedby relative movement of the plates, an

ionizable gas between the plates and contacts, said plateshavingconductive surfaces in opposed relationship free of an intervening soliddielectric barrier, thereby to prevent accumulation of stray chargebetween the plates, a power source adapted to be connected to anddisconnected from the plates and having a high-voltage output of no lessthan about one thousand volts, resistance means of at least one megohmin series with the plates and power supply, and means permitting limitedconduction while preventing complete discharge between the plates uponrelative movement toward one another,

thereby to hold the plates by electrostatic force while tric barrier onwhich stray charge rriight accumulate, a power source adapted to beconnected to and disconnected from the plates and having a predeterminedhighvoltage output of no less than about one thousand volts," resistancemeans of at least one megohm in series with the plates and power supply,and means preventing thess. and f th mo b e gfirqm ,ar r es i s hgs hcplate so closely as to permit conduction between said end areas at saidpredetermined voltage while permitting limited conduction between otherareas of the plates, thereby permitting electrostatic force to hold theplates together while said power source is connected thereto, and meanseffecting relative movement of the plates away from one another uponremoval of the applied voltage.

3. Electrostatic relay apparatus comprising a pair of opposed fullyconductive plates mounted for relative movement toward and away from oneanother, a pair of cooperating contacts at least one of which ismechanically actuated by relative movement of the plates, said plateshavint conductive surfaces in opposed relationship free of anintervening dielectric barrier on which stray charge might accumulateand so that a condition of conduction may develop between the plates, ahigh-voltage power source adaptedto be connected to and disconnectedfrom the plates, a first resistive element of at least one megohmconnected in series with the plates and power source, and a secondresistive element of at least one megohm connected in parallel with thepower source and plates, said two resistive elements being arranged tolimit the current fiow between the plates both when the power supply isconnected thereto and when the power supply is disconnected therefrom,thereby to prevent the plates from being actuated by stray leakage butpermit actuation of the plates when the power source is con nected anddisconnected.

4. Electrostatic relay apparatus comprising a pair of opposed fullyconductive plates mounted for relative movement toward one another froma predetermined released to a predetermined actuated position, saidrelay apparatus having contacts mechanically actuated by relativemovement of the plates, said conductive plates being in opposedrelationship without an intervening dielectric barrier on which straycharge may accumulate, means permitting predetermined areas of theplates to approach one another more closely than other areas, a powersource associated with said plates and having an output voltagesufiiciently high to permit conduction between the relatively closelyspaced areas of plates in their actuated position, and at least one ofthe plates having resistance material to maintain a voltage drop at saidrelatively widely spaced areas of the plates relative to said closelyspaced conducting areas, thereby to hold the plates in the actuatedposition upon conduction between said relatively closely spaced areas.

5. Electrostatic relay apparatus comprising a pair of opposed conductiveplates mounted for relative movernent toward and away from one anotherfrom a released to an actuated position, said relay apparatus havingrelatively movable contacts actuated from a predetermined normally-openposition to a predetermined normally-closed position by relative platemovement, an ionizable gas between the plates and contacts, the closingforce on said contacts being that developed by electrostatic attractionbetween the plates, and a high-vole age power source of at least onethousand volts associated with said contacts, the voltage of said powersource being sufficiently low to prevent conduction between the contactswhen in their relative normally-open position andresistive means of atleast one megohm in series with said contacts to limit current flowbetween the contacts.

6. In an electrostatic control of the character set forth wherein a pairof conductive plates are mounted for relative electrostatic attraction;the improvement that comprises one of said plates being of a resistivecharacter such as to have a high resistance in the direction parallel tothe surface thereof, said resistive plate being in part conductivelycooperable with said other plate at a predetermined locus spacedinwardly from one margin of said resistive plate, and exciting meansconnected to said resistive plate outwardly of said locus of conductionand to said other plate, thereby to cause current flow through theresistive plate to be substantially parallel to the surface thereof andto produce a voltage drop across the surface of the resistive plate, thespace between the plates being free of a solid dielectric barrier.

7. In an electrostaticcontrol of the character set forth wherein a pairof conductive plates are mounted for relative electrostatic attraction;the improvement that comprises one of said plates being relatively rigidand of a resistive character and said other plate being relativelymovable and being hinged along one margin thereof for movement towardand away from said rigid resistive plate, means preventing said oppositemargin of the movable plate from contacting the fixed plate, and plateexciting means connected to the movable plate at its hinged margin andto the rigid resistive plate along the margin thereof which is mostremote from said hinged margin of the movable plate, the space betweenthe plates being free of a solid dielectric barrier.

8. In an electrostatic control of the character set forth wherein a pairof conductive plates are mounted in spaced relationship for relativemovement toward one another in response to the application of anelectrical potential thereto; the improvement that comprises one of saidplates being relatively fixed and the other plate being mounted oppositesaid fixed plate with its center area movable toward said fixed plateinto conductive relationship therewith, plate exciting means connectedto end portions of said respective plates at points remote from saidcenter areas, and at least one of said plates being formed of resistivematerial so as to develop a voltage drop between the center and endareas thereof when the plates move into conductive relationship with oneanother, the space between the plates being free of a solid dielectricbarrier.

9. Electrostatic control apparatus comprising a pair of relatively fixedplates mounted in opposed spaced relationship from one another,relatively movable plate means extending therebetween and having opposedconductive surfaces conductively cooperable with the respective fixedplates, at least one of each pair of conductively cooperable surfaceshaving means preventing complete discharge therebetween but the platesbeing free of an intervening solid dielectric barrier, cooperatingcontacts mounted for actuation by the movable plate, a DC.

' power supply having one terminal relatively permanently connected toone of said fixed plates and another terminal relatively permanentlyconnected to the other fixed plate so that the fixed plates are atopposite potentials, and a circuit including a switch means forintermittently connecting the movable plate to one of the two terminalsof the power supply and a circuit including resistance means of at leastone megohm permanently connecting the movable plate to the otherterminal of the power supply.

10. Electrostatic relay apparatus comprising a pair of fixed platesmounted in opposed spaced relationship and a relatively movable platemeans extending therebetween, but the plates being free of anintervening solid dielectric barrier, cooperating contacts mounted foractuation by the movable plate, means preventing complete dischargedirectly between the plates, a power supply of at least one thousandvolts having one terminal relatively permanently connected to one fixedplate and another terminal relatively permanently connected to the otherfixed plate, a control circuit including switch means for intermittentlyconnecting one of the terminals of the power supply to the movableplate, and a release circuit including resistance means of at least onemegohm relatively permanently connecting the movable plate to the otherterminal of said power supply.

11. An electrostatic valve device comprising a fixed conductive plateand a relatively movable conductive plate mounted opposite said fixedplate, said plates being free of an intervening dielectric barrier, amovable contact carried by and forming a conductively-associated part ofsaid movable plate, a cooperating relatively fixed contact mountedopposite the movable contact and clear of the fixed plate for conductiveengagement by the movable contact, a power supply, an input circuitincluding switch means connecting one pole of the power supply to themovable plate, and an output circuit leading from said fixed contact tosaid other pole of the power supply, said other pole also beingconnected to said fixed plate, and a resistive current permanentlyconnected in parallel with the two plates, and means preventing completedischarge directly between the plates as the movable plate moves towardthe fixed plate.

12. An electrostatic memory device for short-term storage of informationcomprising a pair of opposed conductive plates mounted for relativemovement toward and away from one another, said plates being free of anintervening dielectric barrier, a pair of relatively movable contactsactuated by relative movement of the plates and at least one of which iselectrically insulated therefrom, a power supply, an input circuitincluding switch means connecting the poles of the power supply to theplates, a release-clear circuit including normally open switch meansconnected in parallel with said plates and the power supply to dischargethe plates, and means otherwise preventing complete discharge directlybetween the plates as they move toward one another.

References Cited in the file of this patent UNITED STATES PATENTS749,775 Lacour Jan. 19, 1904 1,446,748 Johnsen Feb. 27, 1923 1,605,911Banneitz Nov. 9, 1926 1,834,786 Kacser Dec. 1, 1931 2,066,211 McCrearyDec. 29, 1936 2,175,354 Lewin Oct. 10, 1939 2,201,879 Blattner May 21,1940 2,269,442 Dench Jan. 13, 1942 2,365,738 Williams Dec. 24, 19442,419,111 Bostwick Apr. 15, 1947 2,466,053 Shaper Apr. 5, 1949 2,786,111Reed Mar. 19, 1957 FOREIGN PATENTS 201,679 Great Britain Aug. 9, 1923

